Penthrox Update
Penthrox, or Methoxyfluorane to give it its official name, has had a bit of a mixed past. But is now becoming recognised as one of the best solutions for emergency pain management for trauma. We’re covering it as a CPD topic because there has been an exciting development in terms of who we can administer it to. But, we’re going to start with a bit of history!
In the 1960s and 1970s, Methoxyflurane was used as an anaesthetic drug, but it was clear there were issues with side effects when it was used in anaesthetic doses and it was found to cause liver and kidney failure on occasion. But as with any medication, the dose is key, and most can be fatal when incorrect high doses are used, but have great therapeutic value at a lower dose.
Penthrox is believed to work by reducing the conduction of pain signals across gap junctions, providing a rapid onset of pain relief in just 6-10 inhalations.
In 2015, Medical Developments International in Australia gained a licence to distribute Penthrox in the UK and Ireland through Galen. Cheshire Search and Rescue team were the first volunteer organisation to adopt Penthrox in 2016, as an alternative to Entonox for adult patients - the size, weight, ease of use and speed of effectiveness being factors in that decision, particularly when compared to Entonox.
It has been seen as the missing link in trauma training for police, firefighters, ambulance services, mountain and other rescue organisations and A&E departments. That said, roll out has been cautious and it is still not carried by all ambulance services, though is increasingly used in A&E departments for orthopedic procedures.
Methoxyflurane is a clear, almost colorless liquid with a characteristic ‘fruity’ odour. It is patient controlled analgesia (under supervision of trained personnel) and administered via a handheld, lightweight and disposable inhaler. It is non-invasive and well tolerated by the majority of patients - though be aware that it can often have a very euphoric effect for some patients. Other common side effects include dizziness, cough (especially with the initial breaths), drowsiness, headache, nausea, feeling drunk and a taste disturbance.
In terms of the safe limit, the dosage administered using the Penthrox inhaler is given at 3 mLs, with a maximum of 6 mLs. This is six times below the anaesthetic safe limit and eight times below the sub-clinical risk of renal failure, where it can only be detected by blood screening. It is only at sixteen times the basic analgesic that levels produce real and potentially long standing renal toxicity. This means the safety margin now is significant.
Indications for use
Penthrox is used for the emergency relief of moderate (4/10 or more) to severe pain, in fully conscious patients with trauma injuries - it is not licensed to use for medical problems. Each inhaler (one dose) lasts 30-60 minutes depending on use and two doses can be given.
And here’s the new development, from June 2026, Penthrox is now licenced and for use for patients of 6 years and older. Though at the time of writing we’re still waiting for MHRA approval in the UK! You can read the research behind this update here.
The manufacturer advises caution if using during pregnancy and while there is no identified risk, they suggest avoiding its use in the first trimester. There are no published studies on the risks during breastfeeding, but current guidelines for anaesthesia and sedation conclude it is compatible with continuing breastfeeding soon after exposure, when the mother feels ready, but not to bedshare for 24 hours after administration.
Contraindications
Age under 6 years old
Recent use - more than 15 mLs in the previous week
Known allergy or hypersensitivity to methoxyflurane or anaesthetic gases
Family history of severe adverse reactions to to inhaled anaesthetics
Personal or family history of malignant hyperthermia
Liver damage or impairment
Chronic kidney disease (Stage 4 o r 5)
Altered level of consciousness from any cause including head injury, drugs, alcohol
Clinically evident cardiovascular instability - hypotensive, arrhythmia, heart failure
Respiratory depression
Set Up and Use
Once you have established that the use of Penthrox is indicated, just follow the instructions to set up the inhaler for use. There are some useful guides in the Penthrox Resources pages on the website.
One useful point to note is that if the supplier is UK based, the inhaler will come with a carbon filter either attached or to be attached. In Australia, the carbon filter is rarely used, particularly if in an outdoor setting.
Pre Administration Checks and Administration Documentation
Inside the Penthrox box you will find the inhaler, a carbon filter, the Methoxyflurane bottle,, a patient information/product leaflet, a patient alert card, the CHECKALL checklist and a plastic bag that seals, for disposal of the used inhaler.
It is important to make sure you go through the checklist before administering and document that this has been done correctly. As for any pain medication, a pain score must be obtained before administering (this is part of the indications) and during/after use to assess effectiveness.
If you see or suspect any adverse effects or events post administration of Penthrox (or any other medication), please report them using the Yellow Card website - you can find the link in resources at the end of this document.
It is also important to remember that there is a training requirement in order to be able to administer Penthrox and it should be covered in your STCW Proficiency in Medical Care qualification or update. Or during bespoke onboard training. If you’re unsure about who can use Penthrox on your vessel, please contact your telemedicine provider and/or Flag State for guidance.
In summary, Penthrox is a lightweight, effective option as an analgesic for moderate to severe pain in trauma patients over 6 years old. It has an excellent safety record and we should certainly consider its use in an emergency for trauma injuries.
We hope you’ve found this Blog useful and picked up a few pointers about Penthrox. Please let us know if there are any topics you would like to see in the future.
The Red Square Medical Team.
References and Resources:
Penthrox Resources - for HCPs - case studies, webinars, research, educational articles
MAGPIE Trial - Penthrox for paediatrics
Comments